chadwick nobel prize

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Beyond the Neutron's Discovery
Significant Events in Science

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Birth of "Nuclear Physics"

Fission - Atomic Age

U-235 (Atomic Bomb)

Quantum Chromodynamics

Chadwick’s discovery of the Neutron led to four significant and subsequent events in science. Following Chadwick’s discovery, German physicist Werner Heisenberg envisioned the nucleus of an atom being constructed of neutrons and protons. This model resolved a number of difficulties, including the problem of the missing mass of the helium atom - two neutrons make up the additional mass, in addition to the two protons. Neutrons also provide an explanation for isotopes, which are atoms of the same element (same number of protons – atomic number) but with different specific masses. The additional mass is a result of the presence of more neutrons in the nucleus. With Chadwick’s discovery of the neutron, and Heisenberg’s model of the atom, an understanding of the structure of the atom and components of the atom was developed. This was the birth of “Nuclear Physics,” – the study of the nuclear structure of the atom.

The discovery of the neutron played yet another key role in history. In 1939, it was discovered that when uranium atoms are bombarded by neutrons, they undergo fission. Physicists quickly learned that this fission would release considerable energy. When it was discovered that the fission process produced additional neutrons, scientists realized that a chain reaction of great power was possible. Hence, the discovery of the neutron ushered in the atomic age.

In contrast with the helium nuclei (alpha rays) which are positively charged and therefore repelled with considerable electrical forces present in the nuclei of heavy atoms, Chadwick’s neutron does not have to overcome the electric barriers (negative, then positive) of atoms, and is therefore capable of penetrating (and splitting) the nuclei of even the heaviest elements. Chadwick, with the neutron, prepared the way towards the fission of uranium 235 and towards the creation of the atomic bomb.

With the discovery of the neutron, the atomic model seemed more complete than ever. Overall charges remained the same, and there was no longer a discrepancy between the atomic mass and the atomic number. But in 1932, only gravity, electricity, and magnetism were known as forces (Electricity and Magnetism would later be combined). It would soon become obvious that there must be a ‘nuclear force’ holding the protons and neutrons together and preventing them from blowing apart due to the columbic forces. It is now known that neutrons play a much more important role within an atom than was originally thought. Decades after this neutral particle’s original discovery it would become clear that both the proton and the neutron seemed to possess equal importance in determining atomic stability. In the 1960’s this theory was refined as the science known as Quantum Chromodynamics which espoused a quark-based theory of the nucleus.